Treatment of pyroligneous acid



Patented Sept. 12, 1944 TREATMENT OF PYROLIGNEOUS ACID Robert M. Isham and Otto Spring, Okmnlgee, 01th., assignors to Danciger Oil & Refineries, Inc., Tulsa, Okla., a corporation of Oklahoma No Drawing.

13 Claim.

This invention relates to the treatment of pyroligneous acid to recover therefrom valuable organic compounds.

In the past, two general methods of treating pyroligneous acid have been employed. In one such method, after preliminary separation of the tar the pyroligneous acid was neutralized with lime to fix the fatty acids as calcium salts and the liquor was distilled to recover methanol. The solution of calcium salts was evaporated to dryness and the residue sold as gray acetate of lime. For the production of free acetic acid this dry product was subsequently distilled with sulphuric acid.

In the second generalmethod of treating pyroligneous acid the pyroligneous acid was demethanolized by thermal distillation and either simultaneously or subsequently the acetic acid was extracted by means of a selective organic solvent.

This second method included two types of sol-' vent extraction treatment; one, of which the Brewster process is representative, involved the use of low boiling solvents such as isopropyl ether; the other type, of which the Suida processis typical, involved the use of high boiling solvents.

In such prior methods, aside from the tar fractions, but two products or fractions were sought to be and in fact were recovered, namely methanol (including methyl acetone and methyl acetatei and acetic acid. I

The present invention is based upon the discovery that crude pyroligneous acid contains, in addition to methanol and acetic acid, other valuable organic compounds which may economically be recovered. In a more specific aspect the crude pyroligneous acid contains valuable compounds, suchas aliphatic lactones and higher phenols which may effectively be removed from the liquor by selective solvent extraction.

In the course of extensive experimentation in this field it has been found that the spent aquecation Serial No. 326,112 filed. on even gate herewith. These valuable products may also be ex- Application March 26, 1940, Serial No. 326,113

present invention is based upon the finding that tracted from the pyroligneous acid simultaneously or contemporaneously with the extraction of the fatty acid content. The present application deals with this latter type of treatment.

It ha been determine that lactones and I analyzing the aqueous solution for butyrolactoneu The following table discloses this percentage of total butyrolactone extracted by the listed solvents when utilizing this procedure.

Table I E 7 Per cent of butgytrolaggne e no Solvent used from 1% a ueous so ution Mxtum of secondary acetate esters, B. P. lilocacti-511i oil fatty ecids... I Secondary butyl acetate Olive oil- Secondary hepty Mixture (equa volumes) of secondary hexyl alcohol and secondary butyl acetate Normal butyl acetate Ethyl oleate Benzene Limpid oil" (a mixture of coal tar hydrocarbons distilling between 218 and 264 C.) Mono-isopropyl naphthalene Naphthene base transformer oil..." gsopriipyl phenyl isopropyl ether.

reso

It will be observed that the solvents chosen for test represent a comprehensive group of organic compounds, including aromatic and aliphatic compounds, alcohols, esters, acids and the like.

' It is also apparent from the results recorded in the table that while marked difierencesin efficiency of the solvents exist a very wide rangeof organic compounds are available under the invention. V

To determine the ultimate concentration of butyrolactone which maybe obtained by countercurrent contactyofcertain or these solvents with dilute butyrolactone solutions, small por- Concentration of butyrolactone in equilibrium with 0.6%

a ueous Solvent The particular solvents listed in Table II were chosen for test because in addition to having a marked solvent power for butyrolactone (as disclosed in Table I) such solvents possessed other desirable attributes of a good selective solvent, namely; substantial insolubility in water, chemical and thermal stability and boiling points which are suiilciently displaced from theboiling points of other valuable constituents of pyroligneous acid to insure eflective separation by simple thermal distillation.

As indicated hereinbefore the prior methods involving the solvent extraction of acetic acid from pyroligneous acid did not contemplate the recovery of selected products, such as the lactones and phenols, nor could such products be extracted in the normal operation of these processes.

In prior processes using a high boiling solvent, such for example as the Suida process, no attempt was made to recover lactones. The solvent dissolved the lactones but the solvent was stripped of the acetic acid and the solvent or stripping oil returned cyclically to the scrubbing column to treat the incoming crude pyroligneous acid. In these circumstances the stripping oil or solvent soon became saturated with lactones and phenols and hence these valuable compounds in the entering pyroligneous acid passed unextracted through the system and were discharged in the waste aqueous liquor.

In the prior processes utilizing the low boiling solvents, such for example as ethyl acetate, any lactones or phenols which were extracted by the solvent remained in the residues after the solvent was distilled oil from the acetic acid. Furthermore, since in these processes no attempt was made to exhaust the aqueous solution of the lactones and phenols a large proportion of these d out of the system in the spent aqueous lquor. In sharp contradistinction to prior art methods in which no attempt was made to recover these valuable components or .pyroligneous acid the present invention comprehends the utilization oi methods and/or materials which positively insure a new result, namely the recovery of these valuable products.

It will be appreciated that the discoveries detially novel or the teachings of the invention may be availed of to modify existing processes to insure as a new result the recovery of the described valuable products.

The first type of improved process may, for the sake of a term, be described as the simultaneous solvent extraction of fatty acids, lactones and phenols and the separation and recovery of these as valuable fractions. For this type 01' process a'solvent having the characteristics 'of -phenyl ethers, such as isopropyl phenyl isopropyl ether serves excellently This product may be made from phenol and propylene according to the method described in U. S. Patent No. 2,104,766. This ether has a boiling range of 262 C. to 270 C., is substantially completely insoluble in water and, as is disclosed in the table, has a high solvent power for the desired extractable constituents; furthermore, the distribution coeflicient between such a solvent and the aqueous phase is most advantageous. A marked advantage inherent in the'use of phenyl ethers is their high boiling point enabling a recovery by thermal distillation of the desired constituents from the liquid solvent phase.

The efficacy of such solvents can the more readily be appreciated by a consideration of a typical test. A quantity of pyroligneous acid containing per liter 57 grams total acid, as acetic acid, and 5.2 grams of lactones was exhaustively extracted with isopropyl phenyl isopropyl ether. The extract was drown off from the extraction vessel, then heated to distill oflf all the dissolved materials and the unvaporized solvent cooled and returned to the extraction vessel. Upon anlysis of the distillate and residual water solution, it was found that substantially all the acids, lactones and phenols were recovered in a substantially anhydrous condition. The distillate was then heated and fractionated up to C. to separately recover acetic, propionic, butyric and valeric acids. The unvaporized residue, having a distillation range between substantially 190 C. and 220 C. and consisting essentially of lactones and phenols, was then subjected to steam distillation after the addition of a small amount of water. The phenols came over with the steam, the vapors were passed through a condenser and the resulting condensate passed to a continuous decanter. The phenol layer in the decanter was discharged to a receiver and the water returned to the distilling system. The aqueous lactone phase, freed from phenols, was then fractionally distilled to separate the water and recover the lactones.

In commercial operations it.is preferred to subject the crude pyroligneous acid to the usual preliminary treatments of tar settling and demethanolizing. It will be understood that if desired pyroligneous acid may be distilled off from a primary still and passed to a scrubbing column. The chose selective solvent may be admitted to the column at an intermediate point and overhead vapors passed to a methanol recovery unit. prising essentially the selective solvent with the dissolved fatty acids, lactones and phenols may then be treated in a continuous cycle to separately recover the constituents of the acid liquor and continuously return the solvent to the scrubbing column. Manifestly the thermal fractionations described may, if desired, be carried out under reduced pressure.

It will be appreciated that while the improved process has been described with respect to a Bottoms from the column com-- single selective solvent a plurality of solvents may be employed.

' It is apparent that the nature of the new improvements presents a wide permissive operative technique. For example, the present improvements may be utilized in a number of different ways to modify processes of the Suida type so as to separately recover the lactones and phenols. As has already been explained, in the Suida process the so-called scrubbing oil soon becomes saturated with lactones and phenols and after this point no longer extracts these components from the entering pyroligneous acid. Such products may effectively and simply be recovered by utilizing the principles of the invention. For example, the solvent oil from which the acetic acid has been distilled and which in the Suida process is returned to the scrubbing column, may be fractionated to separate and recover the lactones and phenols, and then returned to the column.

The improved results described herein may be attained in processes utilizing a low boiling solvent by specially treating the fatty acid residues remaining after distilling on the solvent from the extract. Such residues may be extracted with a selective solvent which has a good solvent power for the lactones and phenols and but a slight solvent power for fatty acids. For example, hydrocarbons like benzene and limpid oil have good solvent power for the lactones and phenols and but slight solvent power for the fatty acids. By extracting these residues with the proper solvent and fractionally distilling the extract, the described valuable fraction may economically be recovered.

The particular solvent which is desirable for a particular process may readily be determined by application of the principles described herein. The choice will be determined by th exigencies of the particular situation in which the process is to be employed. As explained, for simultaneou extraction of both fatty acids, lactones and phenols, a solvent having good solvent power for all of these fractions is desirable. Examples of this type are cresols and other higher phenols, aliphatic esters and ethers, phenyl ethers and the like. The boiling point of the cresols lies quite near those of butyrolactone and valerolactone and they are quite soluble in water. Hence, while these compounds may be used successfully, they are not to bepreferred as against a solvent like isopropyl phenyl isopropyl ether. Again such esters as butyl and amyl acetate will extract all of thevdescribed constituents of pyroligneous acid although the fractionation of the extract involves some diificulties. Hence while definite preference for certain solvents has been expressed it is to be understood that this preference i based on optimum criteria and not on a restricted or exclusive operability.-

It will readily be appreciated that in utilizing the principles of the present invention extraction of the desired constituents from the pyroligneous acid may be carried out in vapor as well as liquid phase.

While specific efiective solvents have been mentioned and while preferred methods of procedure have been described, it is to be understood that these are to be considered as exemplary and not as restrictive for the invention is considered to comprehend broadly the concept of recovering valuable but heretofore wasted products by selective solvent extraction.

We claim:

1. A process: of treating pyroligneous acid which comprises removing tar from the acid, distilling the acid to separate a methanol fraction, treating residual acid with a water-immiscible selective organic solvent phase to extract fatty acids, lactones and phenols and separating and recovering the acids, lactones, phenols and solvent from each other by thermal distillation.

2. A process of treating pyroligneous acid which comprises removing tar from the acid, distilling the acid and contacting the vapors with a water-immiscible organic solvent phase which preferentially extracts fatty acids, lactones and phenols from the acid in water-free condition, removing a vaporous methanol fraction from the upper portion of the column and the extract from a lower portion of the column and distilling the extract to recover a lacton fractio therefrom as a residue.

3. A method of treating pyroligneous acid which comprises distilling crude pyroligneous acid to vaporize constituents thereof which are more volatile than the soluble tar fraction, contacting the vapors with a water-immiscible solvent oil which preferentially extracts fatty acids, phenols and lactones; separating a vaporous methanol fraction and a water-free extract fraction, and distilling the extract fraction to separately recover fatty acids as a distillate, and, phenols and lactones as a residue,

4. A method of treating pyroligneous acid which comprises distilling crude pyroligneous acid to vaporize constituents thereof which are more volatile than tar, contacting the vapors with a water-immiscible solvent oil which preferentially extracts fatty acids, phenols and lactones; separating a vaporous methanol fraction and a condensed solvent water free extract fraction, and distilling the extract fraction to separately recover fatty acids as a distillate, and phenols and lactones as a residue.

5. A continuous process of treating pyroligneous acid which comprises distilling crude pyroligneous acid to vaporize constituents lighter than tar, contacting the vapors with a high boiling water-immiscible organic solvent which preferentially extracts fatty acids, phenols and lactones, controllingsuch contact so as to separate a vaporous methanol fraction and a liquid solvent extract fraction, distilling the extract to separately recover therefrom a distillate of fatty acids, phenols and lactones and a solvent residue, and returning the stripped solvent to the distillation zone for further extraction.

6. A process of treating pyroligneous acid which comprises contacting pyroligneous acid with a low boiling substantially water-immiscible organic solvent which preferentially extracts fatty acids, phenols and lactones in a water-free solution from the pyroligneous liquor, heating the extract to distill off the solvent, then distilling the unvaporized residue to vaporize the recover fatty acid, and leave phenol and lactone fraction as a residue; steam distilling the said phenol-lactone residue to recover aqueous phenols as a distillate and aqueous lactones as a residue.

7. A process of treating pyroligneous acid which comprises contacting .pyroligneous acid with a low boiling organic solvent which preferentially extracts fatty acids, phenols and lactones, fractionally distilling ed and condensing the solvent and fractionally distilling the unvaporized residue to separately recover the fatty limpid oil to extract fatty acids, phenols and lactones, separating the extract from the Wrongneous liquor and fractionally distilling fatty acids, phenols and lactones from the extract.

9, A process of treating pyroligneous acid which comprises removing. the tarry fraction from the acid, distilling the acid to separate a methanol. fraction therefrom, contacting the residual acid with a low boiling selective organic solvent of the group consisting of benzene and limpid oil to extract fatty acids, phenols and lactones, separating the extract from the py oligneous liquor, fractionally distilling fatty acids, phenols and lactones from the solvent and recycling the stripped solvent for further contact with fresh pyroligneous acid.

10. A process of treating pyroligneous acid to recover a plurality of valuable products therefrom which comprises contacting demethanolized pyroligneous acid with a low boiling elective organic solvent of the group consisting of benzene and limpid oil, which preferentially extracts fatty acids, phenols and lactones from the pyroligneous acid liquor, separating. the solvent extract phase from the pyroligneous liquor, fractionally distilling the extract to vaporize the solvent and fractionally distilling the residue to recover separate fractions of fatty acids, phenols and lactones.

11. Method according to claim .3 in which the phenol-lactone residue is steam distilled to give an aqueous phenol distillate and an aqueous lactone residue, and separately dehydrating the recovered phenols and lactones.

12. Process according to claim 5 in which the organic solvent is of the group consisting of phenyl ethers.

13. Process according to claim 5 in which the organic solvent is isopropyl phenyl isopropyl ether.

ROBERT M. ISHAM. O'I'I'O SPRING. 

